# std::ranges::uninitialized_move, std::ranges::uninitialized_move_result

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< cpp‎ | memory

Defined in header `<memory>` |  |
Call signature |  |
template< std::input_iterator I, std::sentinel_for<I> S1, no-throw-forward-iterator O, no-throw-sentinel-for<O> S2 > requires std::constructible_from<std::iter_value_t<O>, std::iter_rvalue_reference_t<I>> uninitialized_move_result<I, O> uninitialized_move( I ifirst, S1 ilast, O ofirst, S2 olast ); | (1) | (since C++20) (constexpr since C++26)
template< ranges::input_range IR, no-throw-forward-range OR > requires std::constructible_from <ranges::range_value_t<OR>, ranges::range_rvalue_reference_t<IR>> uninitialized_move_result<ranges::borrowed_iterator_t<IR>, ranges::borrowed_iterator_t<OR>> uninitialized_move( IR&& in_range, OR&& out_range ); | (2) | (since C++20) (constexpr since C++26)
Helper types |  |
template< class I, class O > using uninitialized_move_result = ranges::in_out_result<I, O>; | (3) | (since C++20)

Let \(\scriptsize N\)N be ranges::min(ranges::distance(ifirst, ilast), ranges::distance(ofirst, olast)).

1) Copies \(\scriptsize N\)N elements from `[`ifirst`,` ilast`)` (using move semantics if supported) to an uninitialized memory area `[`ofirst`,` olast`)` as if by

for (; ifirst != ilast && ofirst != olast; ++ofirst, (void)++ifirst)
`` ::new (`voidify`(*ofirst))
`` std::remove_reference_t<std::iter_reference_t<O>>(ranges::iter_move(ifirst));
return {std::move(ifirst), ofirst};

If an exception is thrown during the initialization then the objects that already constructed in `[`ofirst`,` olast`)` are destroyed in an unspecified order. Also, the objects in `[`ifirst`,` ilast`)` that were already moved, are left in a valid but unspecified state.
2) Equivalent to return ranges::uninitialized_move(ranges::begin(in_range), ranges::end(in_range),
ranges::begin(out_range), ranges::end(out_range));.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

### Parameters

ifirst, ilast | - | iterator-sentinel pair denoting the input range of elements to move from
in_range | - | the input range of elements to move from
ofirst, olast | - | iterator-sentinel pair denoting the output range to initialize
out_range | - | the output range to initialize

### Return value

As described above.

### Complexity

Linear in \(\scriptsize N\)N.

### Exceptions

Any exception thrown on construction of the elements in the destination range.

### Notes

An implementation may improve the efficiency of the `ranges::uninitialized_move`, e.g. by using ranges::copy_n, if the value type of the output range is TrivialType.

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_raw_memory_algorithms` | `202411L` | (C++26) | constexpr for specialized memory algorithms, (1,2)

### Possible implementation

    struct uninitialized_move_fn
    {
        template<std::input_iterator I, std::sentinel_for<I> S1,
                 no-throw-forward-iterator O, no-throw-sentinel-for<O> S2>
            requires std::constructible_from<std::iter_value_t<O>,
                                             std::iter_rvalue_reference_t<I>>
        constexpr ranges::uninitialized_move_result<I, O>
            operator()(I ifirst, S1 ilast, O ofirst, S2 olast) const
        {
            using ValueType = std::remove_reference_t<std::iter_reference_t<O>>;
            O current{ofirst};
            try
            {
                for (; !(ifirst == ilast or current == olast); ++ifirst, ++current)
                    ::new (static_cast<void*>(std::addressof(*current))))
                        ValueType(ranges::iter_move(ifirst));
                return {std::move(ifirst), std::move(current)};
            }
            catch (...) // rollback: destroy constructed elements
            {
                for (; ofirst != current; ++ofirst)
                    ranges::destroy_at(std::addressof(*ofirst));
                throw;
            }
        }

        template<ranges::input_range IR, no-throw-forward-range OR>
            requires std::constructible_from<ranges::range_value_t<OR>,
                                             ranges::range_rvalue_reference_t<IR>>
        constexpr ranges::uninitialized_move_result<ranges::borrowed_iterator_t<IR>,
                                                    ranges::borrowed_iterator_t<OR>>
            operator()(IR&& in_range, OR&& out_range) const
        {
            return (*this)(ranges::begin(in_range), ranges::end(in_range),
                           ranges::begin(out_range), ranges::end(out_range));
        }
    };

    inline constexpr uninitialized_move_fn uninitialized_move{};

### Example

Run this code

    #include <cstdlib>
    #include <iomanip>
    #include <iostream>
    #include <memory>
    #include <string>

    void print(auto rem, auto first, auto last)
    {
        for (std::cout << rem; first != last; ++first)
            std::cout << std::quoted(*first) << ' ';
        std::cout << '\n';
    }

    int main()
    {
        std::string in[]{"Home", "World"};
        print("initially, in: ", std::begin(in), std::end(in));

        if (constexpr auto sz = std::size(in);
            void* out = std::aligned_alloc(alignof(std::string), sizeof(std::string) * sz))
        {
            try
            {
                auto first{static_cast<std::string*>(out)};
                auto last{first + sz};
                std::ranges::uninitialized_move(std::begin(in), std::end(in), first, last);

                print("after move, in: ", std::begin(in), std::end(in));
                print("after move, out: ", first, last);

                std::ranges::destroy(first, last);
            }
            catch (...)
            {
                std::cout << "Exception!\n";
            }
            std::free(out);
        }
    }

Possible output:

    initially, in: "Home" "World"
    after move, in: "" ""
    after move, out: "Home" "World"

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 3870 | C++20 | this algorithm might create objects on a const storage | kept disallowed

### See also

ranges::uninitialized_move_n (C++20) | moves a number of objects to an uninitialized area of memory (algorithm function object)
uninitialized_move (C++17) | moves a range of objects to an uninitialized area of memory (function template)

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